Field of the Invention
The invention relates to medium duty vehicles and heavy-duty vehicle trucks and tractor-trailers. More particularly, the invention is directed to an air-ride axle/suspension system for a medium-duty or heavy-duty vehicle. More specifically, the invention is directed to a multiple lobe damping convoluted air spring for air-ride axle/suspension systems of medium-duty or heavy-duty vehicle trucks and tractor-trailers. More particularly, the multiple lobe damping convoluted air spring includes a rigid lobe having an internal chamber that is in fluid communication with the other lobes via at least one opening formed through the wall(s) of the chamber and adjacent lobes. This structure and arrangement provides restricted airflow between the chamber and the lobes in order to promote damping of the convoluted air spring during operation of the vehicle at a first frequency range, and the rigid lobe includes a mass that promotes mass damping of the convoluted air spring during operation of the vehicle at a second frequency range.
Background Art
The use of air-ride trailing and leading arm rigid beam-type axle/suspension systems has been very popular in the heavy-duty truck and tractor-trailer industry for many years. Although such axle/suspension systems can be found in widely varying structural forms, in general their structure is similar in that each system typically includes a pair of suspension assemblies. In some heavy-duty vehicles, the suspension assemblies are connected directly to the primary frame of the vehicle. In other heavy-duty vehicles, the primary frame of the vehicle supports a subframe, and the suspension assemblies connect directly to the subframe. For those heavy-duty vehicles that support a subframe, the subframe can be non-movable or movable, the latter being commonly referred to as a slider box, slider subframe, slider undercarriage, or secondary slider frame. For the purpose of convenience and clarity, reference herein will be made to main members, with the understanding that such reference is by way of example, and that the present invention applies to heavy-duty vehicle axle/suspension systems suspended from main members of: primary frames, movable subframes and non-movable subframes.
Specifically, each suspension assembly of an axle/suspension system includes a longitudinally extending elongated beam. Each beam typically is located adjacent to and below a respective one of a pair of spaced-apart longitudinally extending main members and one or more cross members which form the frame of the vehicle. More specifically, each beam is pivotally connected at one of its ends to a hanger which in turn is attached to and depends from a respective one of the main members of the vehicle. An axle extends transversely between and typically is connected by some means to the beams of the pair of suspension assemblies at a selected location from about the mid-point of each beam to the end of the beam opposite from its pivotal connection end. The beam end opposite the pivotal connection end also is connected to an air spring, or its equivalent, which in turn is connected to a respective one of the main members. A height control valve is mounted on the main member or other support structure and is operatively connected to the beam and to the air spring in order to maintain the ride height of the vehicle. A brake system and one or more shock absorbers for providing damping to the axle/suspension system of the vehicle in those situations where the air spring is of the non-damping variety also are mounted on the axle/suspension system. The beam may extend rearwardly or frontwardly from the pivotal connection relative to the front of the vehicle, thus defining what are typically referred to as trailing arm or leading arm axle/suspension systems, respectively. However, for purposes of the description contained herein, it is understood that the term “trailing arm” will encompass beams which extend either rearwardly or frontwardly with respect to the front end of the vehicle.
In an alternative configuration, each suspension assembly of the axle/suspension system may include a pair of longitudinally extending elongated beams spaced above and below one another in a generally parallelogram configuration. Each one of the pair of beams is pivotally connected to a hanger at the front end of each beam. Each of the upper and lower trailing beams is pivotally connected to an axle assembly at the rear end of each beam. The upper and lower trailing beams form a parallelogram, or modified parallelogram type of suspension system. Thus, two hangers and two each of the upper and lower trailing beams are provided in the axle/suspension system, one of each on each lateral side of the axle/suspension system.
The axle/suspension systems of the heavy-duty vehicle act to cushion the ride, dampen vibrations and stabilize the vehicle. More particularly, as the vehicle is traveling over the road, its wheels encounter road conditions that impart various forces, loads, and/or stresses, collectively referred to herein as forces, to the respective axle on which the wheels are mounted, and in turn, to the suspension assemblies that are connected to and support the axle. In order to minimize the detrimental effect of these forces on the vehicle as it is operating, the axle/suspension system is designed to react and/or absorb at least some of them.
These forces include vertical forces caused by vertical movement of the wheels as they encounter certain road conditions, fore-aft forces caused by acceleration and deceleration of the vehicle, and side-load and torsional forces associated with transverse vehicle movement, such as turning of the vehicle and lane-change maneuvers. In order to address such disparate forces, axle/suspension systems have differing structural requirements. More particularly, it is desirable for an axle/suspension system to be fairly stiff in order to minimize the amount of sway experienced by the vehicle and thus provide what is known in the art as roll stability. However, it is also desirable for an axle/suspension system to be relatively flexible to assist in cushioning the vehicle from vertical impacts, and to provide compliance so that the components of the axle/suspension system resist failure, thereby increasing durability of the axle/suspension system. It is also desirable to dampen the vibrations or oscillations that result from such forces. A key component of the axle/suspension system that cushions the ride of the vehicle from vertical impacts is the air spring, while a shock absorber typically provides damping characteristics to the axle/suspension system.
The typical air spring of the type utilized in heavy-duty air-ride axle/suspension systems can be of the rolling lobe type or the convoluted type. The rolling lobe type air spring includes three main components: a flexible bellows, a piston and a bellows top plate. The bellows is typically formed from rubber or other flexible material, and is operatively mounted on top of the piston. The piston is typically formed from steel, aluminum, fiber reinforced plastics or other rigid material, and is mounted on the rear end of the top plate of the beam of the suspension assembly by a pedestal and fasteners, which are generally well known in the art. The volume of pressurized air, or “air volume”, that is contained within the air spring is a major factor in determining the spring rate of the air spring. More specifically, this air volume is contained within the bellows and, in some cases, the piston of the air spring. The larger the air volume of the air spring, the lower the spring rate of the air spring. A lower spring rate is generally more desirable in the heavy-duty vehicle industry because it provides a softer ride to the vehicle during operation. Typically, the piston either contains a hollow cavity, which is in communication with the bellows and which adds to the air volume of the air spring by allowing unrestricted communication of air between the piston and the bellows volumes, or the piston has a generally hollow cylindrical-shape and does not communicate with the bellows volume, whereby the piston does not contribute to the air volume of the air spring.
The convoluted type air spring includes three main components: a flexible bellows, a top plate and a bottom plate. The bellows is typically formed from rubber or other flexible or elastic material, and is operatively mounted at its top end to the top plate and at its bottom end to the bottom plate of the air spring. The top plate is connected to an air spring bracket that is in turn mounted to the main member of the vehicle. The top plate can also be directly connected to the main member of the vehicle without use of the air spring bracket. The bottom plate of the air spring is mounted on the axle assembly of the axle/suspension system. The volume of pressurized air, or “air volume”, that is contained within the air spring is a major factor in determining the spring rate of the air spring. More specifically, this air volume is contained within the bellows for a convoluted air spring. The larger the air volume of the air spring, the lower the spring rate of the air spring. A lower spring rate is generally more desirable in the heavy-duty vehicle industry because it provides a softer ride to the vehicle during operation. The convoluted type of air spring is typically utilized in applications where the spacing or clearance between the suspension assembly and the main member of the vehicle is insufficient to allow for the rolling lobe type of air spring.
For both types of air springs described above, the air volume of the air spring is in fluid communication with an air source, such as an air supply tank, and also is typically in fluid communication with the height control valve of the vehicle. The height control valve, by directing air flow into and out of the air spring of the axle/suspension system, helps maintain the desired ride height of the vehicle.
Prior art air springs such as the ones described above, while providing cushioning to the vehicle cargo and occupant(s) during operation of the vehicle, provide little if any damping characteristics to the axle/suspension system. Such damping characteristics are instead typically provided by a pair of hydraulic shock absorbers, although a single shock absorber has also been utilized and is generally well known in the art. Each one of the shock absorbers is mounted on and extends between the suspension assembly of the axle/suspension system and the main member of the vehicle. These shock absorbers add complexity and weight to the axle/suspension system. Moreover, because the shock absorbers are a service item of the axle/suspension system that will require maintenance and/or replacement from time to time, they also add additional maintenance and/or replacement costs to the axle/suspension system.
For heavy-duty vehicle trucks and trailers, the frequencies where optimal damping of the axle/suspension system(s) is critical are from about 1.8 Hz, body bounce mode, to about 13 Hz, wheel hop mode. At these natural frequencies, the axle/suspension system is predisposed to move, so road inputs at these frequencies can result in a build-up of movement in the axle/suspension system that can potentially adversely affect the performance of the axle/suspension system. Therefore, it is critical to provide damping across all critical frequencies in order to promote optimal performance of the heavy-duty vehicle.
The amount of cargo that a vehicle may carry is governed by local, state, and/or national road and bridge laws. The basic principle behind most road and bridge laws is to limit the maximum load that a vehicle may carry, as well as to limit the maximum load that can be supported by individual axles. Because shock absorbers are relatively heavy, these components add undesirable weight to the axle/suspension system and therefore reduce the amount of cargo that can be carried by the heavy-duty vehicle. Depending on the shock absorbers employed, they also add varying degrees of complexity to the axle/suspension system, which is also undesirable.
Certain prior art air springs of the rolling lobe variety have been designed to provide damping characteristics to the air spring. One such damping rolling lobe type air spring is shown and described in U.S. Pat. No. 8,540,222, which is owned by Hendrickson USA, L.L.C.
In addition, a prior art convoluted air spring has been designed to provide damping characteristics utilizing an external tank. That convoluted air spring is shown and described in U.S. Pat. No. 9,139,061, which is owned by the assignee of the instant application.
Although useful for its intended purpose, the damping convoluted air spring of the '061 patent requires additional tanks and conduits that can reduce the amount of space available to the axle/suspension system. Moreover, the external conduits can become damaged by road debris during operation of the heavy-duty vehicle, which can potentially affect the operation and damping of the convoluted air springs and can also require repair that can potentially increase maintenance costs of the axle/suspension system.
The damping convoluted air spring for medium-duty or heavy-duty vehicles of the present invention overcomes the problems associated with prior art damping and non-damping convoluted air springs by providing a damping convoluted air spring that is self-contained, resulting in an air spring that has damping characteristics optimized across the entire critical frequency range while using generally fewer and smaller parts than prior art damping convoluted air springs that include external tanks and the like. The damping convoluted air spring for medium-duty or heavy-duty vehicles includes a rigid lobe that forms an intermediate chamber within the bellows of the air spring that is in fluid communication with the upper and lower lobes of the air spring, to provide restricted airflow between the lobes of the air spring and the intermediate chamber in order to provide damping characteristics to the air spring at a first frequency range. These damping characteristics provided by restricted airflow can be tuned for a given application, based upon the intermediate chamber volume, the volume of the upper and lower lobes, and the size, shape, length, and/or number of openings formed between and communicating with the lobes and the intermediate chamber of the air spring. The rigid lobe also includes a mass. The rigid lobe is connected or suspended between and by the pliable upper and lower lobes of the air spring bellows. In response to the motion of an axle assembly of an axle/suspension system mounted on the vehicle, either in a jounce or rebound event, the rigid lobe moves generally opposite or counter to the motion of the axle assembly due to the inertia of the rigid lobe mass. The generally opposite, counter, or out of phase motion of the rigid lobe dissipates the motion energy of the axle assembly, thereby providing mass damping characteristics to the convoluted air spring at a second frequency range. The mass damping characteristics provided by the mass of the rigid chamber can be tuned for a given application, based upon the rigid lobe mass as well as the stiffness or pliability of the lobes to which the rigid lobe mass is connected and the volumes of air the pliable lobes contain.
By providing a damping convoluted air spring for medium-duty or heavy-duty vehicles that exhibits damping features, the shock absorber(s) of the axle/suspension system can be eliminated or its size reduced, reducing complexity, saving weight and cost, and allowing the vehicle to haul more cargo. Moreover, elimination of the external tank, valves and hardware of the prior art damping convoluted air spring potentially eliminates costly repairs and/or maintenance costs associated with these more complicated systems, as well as reducing weight. In addition, the damping convoluted air spring for vehicles of the present invention can provide damping in certain applications that, in the past, had not utilized shock absorbers, and instead allowed the axle/suspension system to operate without damping, thereby increasing the life of the axle/suspension system and its component parts by reducing excessive wheel bounce during operation of the vehicle. Further, the damping convoluted air spring of the present invention provides damping characteristics optimized across all critical frequency ranges: at a first frequency range, damping is promoted by the restricted airflow between the rigid chamber and the lobes; and at a second frequency range, mass damping is promoted by the rigid lobe mass motion which is generally opposite or counter to the motion of the axle/suspension system.